Devero (Italy) and Binntal (Swiss)
The Cervandone mountain area between the Italian Alpe Devero, and the Binntal on Swiss territory is one of the most remarkable mineral locations in the Alpin Region within the last 30 years. The Cervandone region is famous for the abundance of special
and unique As minerals. The occurrence is the result of a coincidence of very peculiar mineralogical and geological factors. Among these we may remember as the most importants the existence of a prealpine (Hercynic) Cu-As concentration in the Gneisses and the Alpine metamorphism producing temperature - pressure conditions that remobilised the As-ores.
The hypothesis is that during Alpin metamorphism the ore concentration in the gneisses were partly dissolved by hydrothermal solutions remobilising As and Cu. In the Cervandone area these solutions precipitate several arsenic minerals within the gneiss fissures. This process created a large variety of uncommon and even unique minerals. All these minerals have a high content in Arsenic and belong to the family of Arseniates. After the new primary minerals, Cafarsite and Asbecasite (new species, 1966), several additional new species have been described : chernovite, agardite, strashimirite, gasparite (new species 1987), Cervandonite (1988), fetiasite (1991). Other typical minerals of the Cervandone area are Anatas, Periclin, Quatz, Sinchisite,
Collecting in this area is hard and requires a deep knowledge of the geological setting of mineralised gneisses as well as of the paragenesis of the different Arseniates and good physical conditions. Collecting areas are difficult to be reached. A minimum of three hours of walk are needed to recah the most accessible locations. Collecting areas elevation spans between 2200 and 2500 mt. and prospecting is possible just during the summer period (from July to September). On the Italian side the collecting area is wide also if very few locations provided the better specimens. Mineralisation occurs in Mt.leone gneiss within fissures .On the Swiss side collecting area are more restricted and just limited mainly to Mt. Cervandone area. On the Italian territory the famous collecting areas are Pizzo Bandiera, Pizzo Cervandone and Cornera Mt,.
Please note that on the Italian territory the collecting area are comprised within the Alpe Devero Natural Park and collecting is nowadays restricted (special permits may be requested from the Crodo Museum) while the Swiss territory collecting is open.
Cervandone area may be reached from the Italian side by Vigezzo Valley from Baceno, Goglio and then following the Enel private road up to Devero Alp. 2h 30' min walk is needed to reach the nearest collecting areas. On the Swiss side the collecting location may be reached with a 3 hrs. walk directly from Binntal.Geology Cervandone Area is characterised by a wide outcrop of Gneisses (Mt. Leone nappe) and of ultramafic rocks. As mineralisation occurs in the Gneiss of Mt. Leone Group. A thin sequence of triassic dolostones lays at the base of Mt. Leone nappe. This triassic dolostones outcrop in the Arbola and Lengebach areas. All the prospecting area of Cervandone for Areseniates is comprised in the Monte Leone Gneisses.
Prospecting in Cervandone area
Arseniates occurs in gneiss fissures. Prospecting has to be driven by the presence of Arseniate indications. Typical paragenesis with Arseniate minerals are Anatas, Hematyte, Fluorite.
Images taken from the book 'I minerali dell'Alpe Devero' by C. Albertini
Main Typical Occurrences
Agardite (Frequent) - Occurs in nice green xls acicular sprays up to 1 mm. on cafarsite xls or in globular aggregates in gneiss fissures. Often it covers the altered cafarsite xls.
Allanite (Rare) - Occurs in nice prismatic xls up to 2-3 mm. in gneiss fissures .
Anatas (Rare) - Cervandone area produced wonderful specimen of Anatas. Perfect semi-transparent xls up to 2 - 2,5 cm have been collected during the years and may be admired in most of Alpine Museums as well as in private collections.
Asbecasite (Rare) - The first finding was of 1963. Yellow-green flattened Xls uo to 15 mm have been collected but more frequently the mineral occurs as yellow crusts associated with Quartz and Cafarsite.
Cafarsite (Uncommon) - It's the most famous minerals of Cervandone area. It Occurs as wonderful ehuedral crystals in gneiss fissures. The most common habitus is the ochtaedron or cube-ochatedron. Cubic habitus is quite uncommon and therefore highly appreciated. Crystal size may range from few mm to over 4-5 cm. Unaltered xls are of a typical dark-brown color sometimes semi-transparent . Most frequently the xls are altered and covered with Agardite
Cervandonite (Ce) (Rare) - It occurs in nice black rosette aggregates up to 1 - 1,2 cm in size. Common size of cervandonite rosettes spans from 1 to 3-4 mm. Typical paragenesis is with Quartz, Albite, Sinchisite.
Chernovite (Rare) - It occurs as transparent yellow- green bipyramidal pseudochtaedrical xls of 1-3 mm in size.
Crichtonite/Senaite (Rare) - It occurs as sharp nice lustous black euhedral xls up 2 mm. associated with the other Arseniates
Fetiasite (very rare) - It occurs as small globular aggregates of few mm in size of red-brown color associated with Cafarsite and Agardite.
Gasparite (very rare) - This very rare Arseniate occurs in mycro rombohedrical yellow-orange xls covering or completely sobstituting the Synchisite xls.
Nb-Rutilo - Rutile is quite frequent in the Gneiss fissures of Cervandone area in typical red xls up to 4-5 mm in size. The area also provides nice xls aggregates of Nb-Rutile of dark brown colour up to 5-6 mmm associated with Cafarsite and other As minerals..
Sinchisite (rare) - It occurs as nice transparent or semi transparent orange xls with a typical bottle-shape uo to 1 cm in size Altered xls are transformed in Gasparite
Strashimirite (very rare). It occurs as fibrous aggregates or crusts of pale green associated with the other arseniates.
Tilasite (rare) . Cervandone areas provides during the years remarkable specimens of this rare Arseniate. Perfect Red-Brown elongated xls up to 1 cm in size have been collected and are probably the best worldwide specimen for the mineral. Common size of Tilasite xls are of some mm. in size
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